We replaced two of the pleated shades in our previous trailer, a Jayco, with venetian blinds. The reason we did so is because the strings were cutting into the bottom rail. It was quite a job and we had to learn a lot as we went, but in the end we made it work.
Generally, the blinds are attached to the valance. You remove the valance first before fixing or replacing the blind. I have fixed blinds quite often, replacing the strings.
If you take the valance in to a blind store, they can custom make something for you. If the new blind has some kind of control along the side, make sure the side valance is not making it impossible to access this. If you bring the old blind in, that might also help.
Right now I have two blinds that require new strings, one of which I have already re-strung at least once before. I am getting tired of this and I am currently looking for other options, like a roll-up blind or something. The string I bought is slightly thinner than what came with the unit, and I don't know if that is the reason it keeps failing.
Good luck, and let us know if you find an option that works for you.